of the solar system, which occupies nearly 165 years in revolving round the sun, at a mean distance of nearly 2,800 millions of miles, or more than thirty times our own. This distance is, however, considerably less than that at which the next planet ought to be placed, according to the empirical law of Bode, so that though that law was taken as the basis of the first calculations made for the purpose of detecting a planet which, unseen, made its existence known by its powerful attraction, much modification in them had to be subsequently made. We have not space here to enter into the long details of the history of the discovery, which are indeed well known to all interested in astronomy, and are given more or less in every modern book on that science. The first idea of the existence of such a planet was started by M. Bouvard, who, on forming his theory and tables of Uranus, found it impossible to reconcile the earlier and later observations, and was led to suspect the existence of some other planet beyond it, producing irregularities in its motion. The possibility of the discovery of such a planet was much discussed, and the problem of predicting its place, so as to enable observers to see it, was taken in hand by Mr. (now Professor) Adams as early as 1843. His final investigation was communicated to the Astronomer Royal in October, 1845. Meanwhile Le Verrier had turned his attention to the subject. His first paper upon it appeared in the Comptes Rendus of the French Academy for November 10, 1845; a second and third (still more complete) on the 1st of June and on the 31st of August, 1846. On the 23rd of September Dr. Galle, then of the Berlin Observatory, received a letter from M. Le Verrier, requesting him to look for the planet at a particular place in the sky, and saying that he thought it would be large enough to be recognized as a planet by its disc. Dr. Galle at once complied, and the same night noticed a star of the eighth magnitude near the place in question which was not marked in the Berlin star-chart (there made by Bremiker). Observations on the following two nights showed by the motion that this was indeed the planet sought. As for a sensible disc (to use Professor Encke's expression with regard to it) it was only to be recognized in appearance as a planet by one who was aware of its nature as such. Meanwhile Mr. Adams's calculations had not remained a dead letter; but Professor Challis, working from them, had commenced a search for the planet over the arc in which those calculations had shown it to be likely that it was situated. It was unfortunate that at the time the resources of the Cambridge Observatory were so taken up that he was not able to spare time to discuss the results of his sweep each day as they were made; for, not being in possession of Bremiker's chart, there was no alternative but to map the arc in question, and to repeat the observations for comparison. Professor Challis's search commenced on the 29th of July, 1846, and terminated, on his hearing of Dr. Galle's discovery, in the following September. On comparing afterwards his own observations inter se, he found that he had in fact observed the planet twice-on the 4th of

August and on the 12th of the same month; moreover, on the 29th of September (after Neptune's discovery by Galle, but before the news of it had reached Cambridge) he noted an object which, from a suspicion that it had a sensible disc, he intended to look for again, when in the meantime he found he had been anticipated at Berlin.

We now come to the planetary discoveries of Mr. Hind, which added so large a number to the previously known list of small planets revolving at various distances between the orbits of Mars and Jupiter. These were all made at the observatory erected by the late Mr. Bishop, in the grounds of his private residence in Regent's Park, London. Mr. Hind commenced a vigorous search with the aid of the star-charts of the Berlin Academy (extending them in certain places where they fell short of the ecliptic limits in declination), in the month of November, 1846. After nine months of scrutiny, a planet was discovered in the constellation Sagittarius, on the 13th of August, 1847 (about six weeks after Hencke's discovery of Hebe), to which the name of Iris was attached. On the 18th of the following October, Flora was found in the same manner. Next spring, Mr. Graham entered the field, at Mr. Cooper's private observatory, at Markree Castle, county Sligo, Ireland, and discovered a planet named Metis, on the 25th of April, 1848. About a year afterwards, Dr. Annibal de Gasparis, assistant at the Royal Observatory at Naples, made his first discovery, and as his, like Mr. Hind's, are many in number, it may be as well to give them in tabular statement, thus :

After this last date, this zealous observer was "rude donatus," and many others had entered into the same field, so much more fertile then had been at first supposed. But we must now give a similar table of Mr. Hind's discoveries in this line :—

A few months after the discovery of the last of this list, the first transatlantic planet was discovered by Mr. Ferguson, at Washington, on the 1st of September, 1854. It was named Euphrosyne; and the same gentleman afterwards discovered

Virginia, on October 4, 1857, and Echo, on September 14, 1860. Mr. Marth was the first discoverer of Amphitrite, on March 1, 1854, at Mr. Bishop's observatory, in Regent's Park. The late M. Chacornac discovered the first (Phocea) of the following six, at Marseilles, and the remaining five whilst he was attached to the Imperial Observatory, at Paris

:-

We may now mention five small planets, each of which has been the sole contribution of its discoverer to our knowledge of the group. They are, Nemausa, discovered by M. Laurent, at the Observatory of Nismes, on the 22nd of January, 1858; Pandora, by Mr. George Searle, at the Observatory of Albany, U.S., on the 10th of September, in the same year; Erato, by Professor Förster, at Berlin, on the 14th September, 1860; Hesperia, by Professor Schiaparelli, at Milan, on April 29, 1861; Freia, by the late illustrious director of the Copenhagen Observatory, Professor D'Arrest, on the 14th November, 1862; and Semele, by Dr. Tietjen, at Berlin, on January 4, 1866.

Coming next to some of the astronomers who have made the largest additions to the list, we have to name first, Dr. R. Luther, of Bilk, near Düsseldorf, who discovered :

Not much less numerous have been the contributions of the late M. Hermann Goldschmidt, and they must be considered amongst the most remarkable from the slender means at his disposal, so that the earlier ones were made with telescopes of very small power, pointed through a window of a garret, in a street in Paris. His list is as follows:

The eighth of these (Melete) was, when it was first discovered, supposed to be Daphne, which had been lost for a time. When it was found out to be a new planet (by the computer of its orbit, Mr. Schubert) it was for a considerable time known as Pseudo-Daphne, in allusion to that fact, until the name suggested by the Greek proverb (μeλétŋ tò πâv,) was chosen for it. In lists of the small planets it usually appears out of place in the order of discovery, it being difficult to disturb the numbers with which later ones had become associated.

Mr. Pogson commenced his small planet discoveries with that of Isis, at Oxford, on the 23rd of May, 1856; and afterwards detected at the same place, Ariadne and Hestia, on the 15th of April, and the 16th of August, 1857. After his removal to the East Indies, as Director of the Madras Observatory, he discovered there four more, Asia, Sappho, Sylvia, and Camilla, on the dates, April 17, 1861, May 2, 1864, May 16, 1866, and November 17, 1868, respectively.

The next who put in the scythe was Herr Tempel, by the discovery at Marseilles, of Angelina, on March 4, 1861, and Cybele (at one time called Maximiliana), on March 9, only five days afterwards. These were followed by Galatea, on August 29, 1862, and Terpsichore, on September 30, 1864. His next and last discovery of this kind was that of Clotho, on February 17,

1868.

Mr. H. P. Tuttle, of Harvard College, Cambridge, U.S., discovered two; Maia, on the 9th of April, 1861, and Clytie, on the 7th of April, 1862.

We now come to the discoveries of the astronomer who has contributed more members to the long list of minor planets than any other, Dr. C. H. F. Peters, of the Hamilton College Observatory, Clinton, U.S. The first of these (Feronia) was detected in the year 1861, accidentally; being very near Maia, then a recent discovery and of which Dr. Peters was making a series of observations, it afterwards appeared from the calculations of Mr. T. H. Safford, that a part of them, commencing with May 29, really related to another planet, hitherto unknown. Beginning then with this, the following are the additions to the small planets made by Dr. Peters, twenty-six in number:

Little more than ten years ago, an observatory was established at Marseilles in connection with the Imperial Observatory at Paris, and M. Stéphan was appointed its director. Under him it has been fruitful in planetary and cometary discoveries, of which we are now only concerned with the former. M. Stéphan discovered one called Julia, on August 6, 1866 ; and one of his assistants, M. Coggia (whose name is so well known as attached to the fine comet seen in the summer of 1874), detected Ægle, on the 17th of February, 1868. The other assistant, M. Borelly, discovered Ægina, on November 4, 1866; Dike, on May 29, 1868; Lydia, on April 19, 1870; Lomia, on September 12, 1871; Lachesis, on April 10, 1872; Lucina, on June 8, 1875, and Dejanira on December 1, 1875.

Another American astronomer now appears upon the scene, Professor Watson, of the Observatory of Ann Arbor, Michigan. His discoveries have been very numerous, and are comprised in the following list :-

The last three of these are as yet unnamed, and are distinguished only by their numbers in a general list. Juewa was discovered at Pekin, where Professor Watson had gone to observe the transit of Venus, in the following December.

The next batch we shall mention consists of eleven found by the brothers Henry, at the Paris Observatory. M. Prosper Henry discovered Liberatrix, on September 12, 1872; Johanna, on November 5 of the same year; Gallia, on August 7, and Bertha on November 4, 1875; and Nos. 162 and 169 (unnamed), on April 21 and September 28, 1876. M. Paul Henry's discoveries are Velleda, on the 5th of November, 1872; Lumen, on the 13th of January, 1875; Atala, on the 2nd of November, of the same year; Emilia, on the 26th of January; and Eva, on the 12th of July, 1876.

Two more planets were each the single contribution of one observer, Protogeneia, found by Dr. Schulhof, of the Imperial Observatory, at Vienna, on July 10, 1875, and Koronis, by Herr Knorre, at Berlin, on January 4, 1876.

A small observatory, established a few years since by the Austrian Government, at Pola, near Trieste, has furnished a considerable quota to the list. Herr Palisa, its director, discovered a planet to which he gave the name of Austria, on the 18th of March, 1874; and followed it on by detecting Melibea, on the 21st of April, and Siwa, on the 13th of October, of the same year. In the following year (1875) he also found Polana, on January